Gas filled thyratron



Oct. 7, 1952 H. D. DOOLITTLE GAS FILLED THYRATRON 2 SHEETS-SHEET 1 Filed June 15 1951 l 2 2 .3 M 5 m w w w B B m 5 M 2 2 .W I.\ 3 I I 5 I I1\ 0 3 w 4 2 \1 I 4 a 7 tn 2 z m w w M B 9: 3 5 H B m m. T F 8 H l O l 2 4 33 3 5 .-H d 3 3 w 4 3 O 5 n 3 4 W o 3 4 2 4/ a\ .w m |T|,\ 1- K @W f 2 3 FIG. 4

FIG. I

FIG. 3

INVENTOR HOWARD D. OOLITTLE L. ATTORNE FIG. 2

Oct. 7, 1952 H. D.DOOLITTLE GAS FILLED THYRATRON 2 SHEETS-SHEET 2 Filed June 15 1951 ml Mun FIG. 7

INVENTOR HOWARD D. DOOLITTLE BY W - ATTORNEY dom paths.

shielding structures.

Patented Oct. 7, 1952 UNITED STATES PATENT j o F-Ica GAS FILLED THYRATRON Howard D.-Doolittle, Stamford, Conn., assignor to Maclilett Laboratories, Incorporated, Springdale, Conn., a corporation of Connecticut Application June 15, 1951, Serial No. 231,772

tween grid and anode is determined by the voltage therebetween. The higher the'voltage the closer the grid-anode spacing must be. If the spacing between any point on the grid and the nearest point on the anode exceeds this minimum value, breakdown will occur between'these points. Itmust also be rememberedin adjustingfspacings. that breakdown tends toiollow lines'oi forcerather than straight-lines or ran- 7 Furthermore, since field emission will occur if these elementsare too close spaced, there i a loweras well'as upper limit to the grid-anode spacing.

Most of the anodes used in the prior arthave been necessarily almostcompletely surrounded by metallic grid potential shielding'means which is also Iplaced"'closely adjacent the .anode at all points to vpreventbreakdown between grid and anode. .Bre akdown between grid and anode or between cathode andfanod'e. 'around the "grid cylinder ratherjthan through the p'erforations'in high'power thyratrons has also been prevented by enclosing the anode lead with a glass tube.

35 Claims. (Cl. 31562) must be fixed in order to avoid breakdownbe- I object I employ a cylindrical anode in combination with a cylindrical active grid. This anode is supported by the vacuum envelope side-walls or,

in the alternative, forms part'of the vacuum wall of my tube. It is advantageously located near the mid-point of the side wall which is composed primarily ofglass or other insulation. The anode encircles the grid cylinder and is thereby shield-'- ed from the cathode which, in turn, is encircled by the grid potential cylinder. One end of this grid cylinder is sealed at one end of the tube to the envelope side walls. The other end of this grid cylinder, by virtue of spring fingers or other v contacting means, slides upon the metallic terminating member of the envelope side walls at the o posite end of the tube. Thus, the only possible conduction path between the cathode and theanode is through the perforations in the active grid. Breakdown between grid and anode 1 is avoided by keeping the efiective length of the discharge path between the grid and anode shorter than the minimum breakdown spacing according to Paschens Law. However, because the anodeis not completely surrounded by' the "grid, and "thegrid cylinder, in fact, has points sufficiently far" from the anode-to permit breakdown, the insulation joinin anode and grid is kept close spaced to the grid cylinder at points remote irom the anode; ,Thus the lines of force will liollow' paths through the high permitivity mate'- rial, rather than through 1 the gas-filled region.

Breakdown cannoto'ccur between grid and anode within the tube through this dielectric fwall. Wall charges on the glass insulation also tend to provide a suitable ,fieldj distribution to prevent breakdown from anode to grid. Outside of the Unfortunately, the necessityv ,of so enclosing the anode within the gridand shielding structure has produced m'any difficulties.

For instance, any conductive cooling'of "the anode has had to be accomplished through; the anode lead which, at best, has been a long heavy rod. Further-- ,more, it has proved expedient touse structures of planar, rather than more complicated shapes, in

order to,a void complication .of the. grid-and I 'Tlhua'ifthe tubespower capacity and anode" radiating areaiwere to, be

increased, it has been necessary to. increase the tube diameter in order'to accommodate a larger 7 planar anode.

'accordinglyit i object of this -inventionitp provide a thyratron suitable fog use at'high power levels having an anode; which is -thoroughly shielded from; the ;c athode and close spaced to the grid In; order to accomplish my pressure.

materially increasing tube size. v v

anode .makes available (a relatively" large anode tube breakdown cannoto'ccur because thelength of., possible paths between grid. {potential mem bers and anode potential membersis well in ex cfess; of the maximum spacing for breakdown 'in the relatively high pressureair at atmospheric It is another objectrof myinvention 'to 'pifo vide' increased tubepower capacity and to "facilif tate'betterheatdisposal from the anode without My c in ie area; An increase in anode r amay be accorn} plished as with the planar: anode by increasing tube diameter, but it may, also be accomplished without increase tube 'diameter-byincr ing the axial length of the anode c'ylind larger anode area permits more radiation of heat, an t e. a o e ation: adja ent" th bb The makes possible -greater; .efiiciency in radiation.

Also the location of the anode either in the vacuum wall or immediately adjacent to the vacuum wall makes possible a short, low heat-flow impedance thermal path for conductive cooling.

Limitations imposed on anodes for use in high power thyratrons have also imposed limitations upon the active grid tructures-(theperforated grid area) which may be employed with them. Overheating of the active grid has been common in prior art structures because of the high impedance thermal paths involved. Long, high heat-flow impedance thermal paths have been necessitated by the larger grid diameters employed.

pands more than the surrounding support portion. This buckling produces a change in the grid-anode spacing which upsets tube characteristics considerably.

Accordingly it is. an, object of -my invention to provide a grid structure in which the perforated active-gr-id -area is'veryshort sothat the. thermal path to areas of high heat conductivity :is decreased. My cylindrical grid. arrangement permits-thisshortening becausethe same amount of. active gr-id..area;as ispresented by a largediameterplanar memberjmay be presented by my relatively narrow ring. Thus. it willbe but a short distance fromthe. middle of.the ac- .tive gridto the support thereof at either end.

It-isano ther object of my inventionto provide a ri d. which .Will .;not. buckle and change the anode-grid, spacing. ,My, invention accomplishes this object by use of-a" grid cylinder one -end. of .yvhichis freertoslide against the conductiveend .portionof the outer wall. 'Thus, as axial expansion of the-,grid'occurs, due, to heating, the spring fingers permit it toslide alongthis-vacuum wall end member, thereby maintaining normal ,gridanodespacing.

.Thejcylindrical gridand anode structure is alsoadvantageous from the standpoint of'asfsernbly. IThe requirementfof enclosingpriorart anodes withinfgrid and shielding means makes it difficult to achieve. accuratealignmentofthese elements. .By' my invention .the anode '1 may be placed ,in i or adj acent to the outer vacuum wall and. accurately. aligned relative ,to the outer wall. V

Thereafter, the grid .cylinder may be placed within the outer .wa1l,.ac,curately aligned .With respect .It'othe andde, andfixed in placetothe outerwall. b

' The .,ease of alignment pf the cylindrical tube parts also makes practical another I novel feature ofmy invention. .This feature consistsof placing auxiliary electrodes between :the' anode and the grid. Auxiliary; electrodes are advantageous in high ,power structures to perform the dual.

functions of dividing the voltage and shielding 'the anode from the grid. Voltage'divisionis of advantagebecause it .makes it v possible j to incr'easethe grid-anode spacingfor a tube ot; given voltage ratinglor to Qiriorease the voltage rating for the .same gridea'node spacing. This is the case ,since, with i the auxiliary electrodes" in use, adjacent electrodes will have less voltage between them so that the minimum breakdown spacing according jto Pascherrsj Law is increased. A thyratron is ,rendered "inoperable when: its ,gas pressure is reducedbelow the level necessary t su port conduction. leakage, adsorption and absorption of the gas account for such reduction j in pressure. liaiticularly significant i the amount of gas adsorbed by the glass or other in- One problem resulting from thermal effects has been buckling of the; grid which 00- curs because the active grid is heated and ex -v sulators during the operation of the tube. Glass has little tendency to adsorb the gas molecules as such, but it readily adsorbs gas ions.

It is therefore another object of my invention to reduce the amount of adsorption and absorption of the gas filling the tube. My invention accomplishes this end in at least three ways. It

reduces the surface area of insulation in the tube; it places the insulation adjacent metallic surfaces so that it is inaccessible to ions; and it reduces the amount of ionization in the normally non-conducting region of the tube. The amount of insulation is reduced by the elimination of the conventional; glass stem and the substitution .101? a tubular cathode sealed to the tubular end portion of the envelope side walls by a small ring of insulation. The metal grid cylinder shields the envelope side walls from ions and the small ring of insulation between cathode and grid is placed, close to metalso thatlittle space is left ffor occupancy by ions. The tubular cathode and terminal structurehas a sufliciently low inductance that the cathode surge voltage produced by current-pulsesin cathode lead ionizes relatively few molecules of gas despite the high rate of change of current involved. Thus only a small amount ofjthe gas in the grid-cathode region adj acent' the insulation is subject to adsorption.

Therate at which firingmay be repeatedis a veryjimportant factor in many thyr'atronuses. Therepetition rate may be and is often quite high for smallpower thyratron s, but, aspower, is increased, the possible repetition rate decreases. This is so because theheayycurrent drawn. during the start of the firing heats the anode more than the current during the remainder. of the firing period which latter period may be much longer. Thus, asheat dissipation capabilities are increased, such. as'they. areby' my invention,lthe repetition rate .may be increased. However; even though anode dissipationisadequate, the repetition rate; is limited by another factor. Before tion to increase the possible repetition .rate in thyratrons by the mOITe, ,rapid' neutralizationof ions. {M invention accomplishes this end .by placing. grid or cathode potential metallic vanes in the, spacebetween cathode and grid. It is most important to place th'ese vanes in the region, ad- 'jacentthe'active grid'wheredonization'is extensive. However, thevanes maybe usedto, advantagein otherportions of thetube-also, The location; and, shape pf the vanes is governe'diby their-purpose, namely to cut down the distance thatfions travel to a neutrali'zling surface' thereby cutting. down on'the 'deionizationtime.

fwhereas use of ,the deionizingvanes minimizes theamount of necessary'baffling in thyratrons it is still'oftn desirable .to employ bafliingfor greatergridcontrol". fBafIli-ng intheprior art has hadthe undesirableief fect of restricting, the conduction currents -'-injthe'tube to limitedjpaths'.

This --is-' so because the conduction streams -tend to confine themselves to paths of approximately equallength. Thus a circular baiile' placeddirectly in front of *a planar active grid has con- =fi'ned conduction currents 'toihose terminating in a-ring on the ari'odei Accordingly; -itis another object of'my 'inv' titirflto betterdistribute the overallloading of't he "andde- I accomplish this object by arranging bafile means to cover individual perforations whichbaiiles terminateat equal distances from their respective perforations so that the conduction path between cathode and anode through any perforation is essentially the same length. That is, I use narrow bafiles'which adequately coverthe perforations' but-not large areas of the impe'rforate regions of" the active grid.

Although the features ofmy invention are conveniently used to advantage with my novel cylindrical'tubegeometrmthey may also beappli'ed in various prior art thyratron structures. Reference tothe following drawings will illustrateadditional advantages and give a'betterunderstanding of my invention:

"Fig.1 shows'insection a preferred form of my novel thyratron structur'ei i Fig.'2'is a-crosssection view of the same tube taken at section 22 of Fig." 1'. 3

Fig. 3 is a cross sectional view of the same tube taken at section 3-3 of Fig. 1. "Fig. 4 shows in partial section an alternative form of my novel thyratron which employs a voltage dividing anode for use in tubes to be operated at higher voltage.

Fig. 5 shows in section an alternative arrangement of deionization vanes in combination with the active grid which'may be substituted for the bafIle-vane structure of Fig. 2'. r' Fig. 6 shows in section still another alternative form of deionization vanes which may be sub- 'stitute d for the bafiie-vane region shown in Fig. 2.

' Fig. 7 shows a single vane of the type employed in the Fig. 6 construction.

Fig. 8 shows a view of the active grid of Fig. '6 without the vanes affixed and with a segment broken away to show how the vanes are fixed to the grid structure. I r

Fig. 9 shows in partial sectiona planar type of thyratron employing some of my novel features including individual baflle means. I

Referringto Fig. 1 the tube illustrated has a tubular anode III which is supported by means of an annular, radially outward extending flange member II to which it is brazed or otherwise permanently affixed. This bange in addition to providing support for the anode offers a large area, low impedance heat flow path from the anode to the outside of the tube envelope. The

flange member is advantageously affixed to the tube envelope -side walls by sandwiching it between the radial portions of annular bracket member's I2 and I3. These bracket members have tubular portions coaxial with the anode which extend in opposite directions from the flange II, thus enabling them to be affixed to the tubular glass sidewall members I4 and I5. It is also possible to make the anode part of the vacuum wall of the tube, but the construction described makes it possible to employ an anode and flange having better conducting qualities and wall portions having a coefficient of expansion close to that of glass in order to obtain better seals.

The'active' grid member I1 consists of'a ring lying coaxially within the tubular anode. This ring maybe very short in axial length and still present the same active grid area as is presented by planar prior art'structures. Thus the heat flow impedance tothe edges of the grid is materially decreased over thyratron grid structures of the prior art. Perforations in the grid are advantageously a single row of parallel elongated slots. These perforations aresuperiorto perforations in prior art grids in that they-are equidistant from the cathode. Thus conduct-ion currents will not tend to favor certain perforations and ignore others since the path length from cathode to anode is the same through every grid slot. Furthermore, the elongation of the perforations prevents point bombardment of the anode by positive ions during inverse voltage periods. Instead, the destructive effect of the bombarding ions will be-distributed along a lineandlhence diminished at any one point.

in thyratrons of theprior art,-the active grid of my tube is affixed to a grid cylinder. (members Is and 20). However in this instancethe active grid I1 is cylindrical itself and actually forms asegment-of the grid cylinder, As in the prior art'it is thefunction of the grid cylinder-to act as a shielding means which prevents discharge between the cathode and the anode other than through the perforations of the active grid. My grid cylinder is made more effective than prior art structures in preventing such improper breakdown in view of the fact-that it is intended to be used at high power levels; Such breakdownis prevented by terminating both ends of the grid cylinder at the vacuum envelope. However, since it is a purpose of my I invention to prevent buckling of the active -grid, both ends of the grid cylinder cannot be fixed to the vacuum wall. Thus by my invention one end of the grid cylinder, an edgeof member 20, isafiixed to the envelope side walls. In order-to permit the use of high conductivity material as grid cylinder member-20, a tubular collar 2| of metal having goodpro pertiesfor glass to metal joints may be usedtoseal --to side wall insulator 'I5. The other end'of the grid cylinder, an edge of member I9," must be flx'e'd in place. In order to insure its freedom tomo've as well as a constant contact with'the envelope side walls, resilient contact means, such as spring fingers 22, is afiixed to member I9. To'avoid the necessity of its contacting the 'insulator "'I4, 'a tubular metallic extension 23 to the envelope side walls is sealedto insulator- I4. The contact between the resilient means22 and the tubular extension 23 permits the use of member 23 as'a grid terminal. The active grid I 'I maybe 'fabricated asan integral part of a one piece grid cylinder; However, it is often desirable to use different niaterials for the various segments of the *grid cylinder. For instance, it is easier to perforate a small strip than a large sheet or cylinder; Furthermore, by using a separate tubular member for grid cylinder segment 20 it is possible to' provide a low impedance heat flow path to the outside of the envelope. It will be noted in thisconnection that, by placing the end wall 24 immediate- 1y adjacent the active grid II, the whole-inner surface of tubular member '20' as well as theend wall -24'is available for convective cooling. 7

The cylindrical geometry of this preferred tube structure lends itself to accuracy in; positioning and alignment. In assembly,for instance, the

anode may be easily aligned for accurate sealing tures, breakdown between grid and-anode would .seem: to bemore probable. The minimum spacingcbetweenanode and cathode whichwill permitsbreakdown for the particular pressureof the particular gas used according to Paschens Law .must; not be exceeded. .However,.:breakdown. is avoided; in my structure by the j judicious positioning-of insulators l4 and I5 which are so shaped that theirspacingifrom' thegrid through- .out: most of ttheirrespective lengths isiin the order of the .1 grideanode spacing at its closest .point. Thus the :lines .of force between the vanodeand portions oftthefgrid-remotefrom the .anode pass through the low permitivity insula- .tionr-which;acts as: a barrier to prevent break- ;downalong such'lines. In addition; the accumuxlation of positive wallcharges onx insulators l4 rand l5 cause lines of forcefrom .the. grid to go 'directlyato the insulators; rather than curving ;.toward-;.theanode.

..-It is.;usually of advantage to use oxide coated .ca'thodes in thyratrons in order to obtain high .electrontemission; The location of the active cathode' areain the thyratron may be considerably varied. I employ a tubular'cathode 21' in my :thyratron which lies within the'grid cylinder ex- :tension 1. I 9, :wel1. removed. fromthe active grid 5,8163. J-Either theouter 'or. inner surface of the .-cathode tube 2! maybe coated with oxide emittter. .-I-Iowever, it seems preferable to -place the emitter. on the inside of the cathode. tube so that theiconduction current is partially diverted 'by .lateral bafile plate or cap-28which may be sup- ..ported on tab supports 29'which are joined to the ..cathode. A tab-30 extendsfrom the center of thebafile plate28 toward the cathode 21. To the end of tab 30 is affixed high inductance'heater .coil 3| which lies withinthecathodecylinder in .a position essentially coaxial with-the cathode. ..The heater is terminated .inaxial-conductor 32. Conductor 32 passes through :an insulating washer-33 which issupported by annular plate 34 :which'is' irr-turn-affixed to the cathode cylinder. The heater lead 32 may be attached toa rod lead .35.-which lies on the'tube axis-coaxially within cathode cylinder 21. .thimblelike member 36 which is composed ofima- .terial which" in turn may betsealed to annular -insulator '3'l. :Insulator31 thus forms the major :portion of the-vacuum wall betweencathodecylinder 21 and heater lead 35. The'cathode cylin- .der 21 and the heater-= lead "arethus brought out. coaxial with grid terminal 23 and extend to anydesired-length, inorder to makeconvenient ;.connections withits circuitry. a

. The tubular member 21 is continuous from the; 7

:outside ofthe vacuum. wall .to the. cathode sur- .,face. Thislarge: diameterv tube efiectively forms a low inductance; lead which replaces the high .inductance leads oitthe prior art. Thusfdespite the high rate of change ofycurrent which. occurs, thesurge voltage pulse .in thecathode. lead. which is: a. product of the lead inductance I and current rate. of change is' materially reducedover: that :in priorart; structures. "Thisjvoltage reduction rtEIldS, .to reduce: the opportunity? for'ziuntimely This rod-may be: sealed to breakdown, but, evenmoreimportant it tendsto decreasethe amount of-ionization; near insulation produced by the -voltagepulse. Furthermore.'it prevents damage to the tubeand minimizes-disturbances in the. related circuitry.

1 311158 current in the heater is undesirable.

Even a small increase in. heater current will greatly increase the. temperature of the filament and hence -its decomposition rate, consequently materiallyishortening.filament. life. Thus 'my filament is-preferably .a high inductance ".coll

connected-at one end to the low inductance-cathode-andoat its 'otherendto asimple rod .or wire whose inductance: is relatively. high-"compared with. the cathode lead. This heater lead' is advantageously located coaxially withinthe cathode terminal with-an insulating member forming part of the vacuum envelope of the=tube1sealed therebetween. Thus itisdifiicultior'. high 'current pulses to get into. the heaterand reduce tube life.

The fact that both-the cathode cylinder "21 and the'members: [-9. and=23- making .up the adjacentgrid lead are tubularand of. low inductance minimizes the amount of.-ionization=-w1'1ich can take place in the region between-cathode'and grid. In fact due to Paschens Law any discharge will tend to take. place between. members [9 and .2! where the-spacingis great, .i.: e., away from glass. However, even if ionsdrift into the region of-the-glass the use oftubulardeads makes it possible to. use a relatively .smallamount of insulation inaring-seal 23 between the .grid potential-side wall member- 23 and-the cathode tube 2! rather than the large amount. of glass conv ntionalin. stem presses, .so that therewill be less-insulationtoadsorb:or absorb ions formed in the region-adjacentthe insulators. My structure avoids the adsorption orabsorptionuof gas ions .bythe insulation notonly: by. reducing the amount of insulation .usedbut also by placing theinsulation insuch locations. that the number .of. stray ions .ableto reach itis greatly. reduced.

Apair of tubularmetallic sleeves. Ml andLM sealed .to.. oppo;site edges otthe insulating ring. 39 com-- In. addition to insulator 3 9 which .1 is also close .-spaced to -memberl23. Llhis spacing. should. .be as close .as .possible -:wi'thout Idefeating the purpose .of .the configuration by permitting breakdown.

Thus it isgdi'fiicult. for. ions. toget into, the. small space between insulatorl 39. andmemberZS. 1 Further- .more.manyionsldrifting. toward this. region will contact sleeve All or memberi Z3 in. the, process v.and. be. neutralized.

'iIfhegrid. leadaglike the cathode. leads .area'dvantageously tubularin' Shape ,and consequently of low inductance. In my .structureconnection to the tubulaiflgrid. structuremay. be .made .at botl1 ends .of'1the' tube. .The' low' inductance of the, grid leads is of. great advantagejbecause it offers; greater control of the tube'throughappropriatecircuitry. ForIinstance it is.- advanta- ..geo,us to limit bylitheuse of. external impedance the feedback into ..the triggering-Ucircuit. This .feedback issproducedbythe high grid voltage .spikein the gridwhich appears due to theconuductivetcouplirig between grid and. anode during initiation-pf. the discharge.

The voltage. spike may be kept OUtwOf'; the: trigger circuit. easily in my tube because any amount or type of impedance may be placed between'the grid and the trigger circuit so that a minimum disturbance for any set of operating conditions may be achieved, and/or an optimum value of impedance maybe selected to make the build up of current between cathode and anode occur under the most favorable trigger conditions.

'- The use of oxide coated cathodes is highly des'irable in thyratrons because of the high emission possible with this type of emitter. Use of the oxide coating, however, involves'the problem of converting carbonates to oxides. This process must be carried on under vacuum conditions to assure the formation of oxides rather than other compounds. During the conversion large quantitles of gas are evolved. These gases are partially adsorbed and absorbed by the grid and the anode with the result that these structures are very difiicult to completely outgas later.

My cathode assembly makes it possible to convert the carbonates to oxides before placing. the assembly in the vacuum envelope with other tube elements. My cathode assembly including the sealing means consisting of insulator 39 and sleeves 40 and 4| may be conveniently sealed into a vacuum envelope without other elements,'and there the carbonates converted to oxides. This may be conveniently done by sealing sleeve 4| to a tubular member similar to member 23 at one end of the temporary envelope using a low 'melt--' ing point solder or by gasketry. After conversion, the seal may be melted and the cathode assembly sealed in place to member 23. a Fig. 2 shows a cross section of Fig. 1 in the active grid region; wherein the anode terminal flange [2, the anode l and the grid I'I are shown" in "section. Closespaced to and coaxial with the grid is baiile ring 43. To this baflle ring are affixed a plurality of inwardly extending metallic deionization vanes 44 which may be of varied length and whose primary object is to present a large amount of grid potential area in the region adjacent the active grid. The function of these vanes is to quickly capture positive ions when conduction current is to be stopped. The preponderance of the ions in the tube accumulate in this region. The neutralization of such ions necessary for the stoppage ofconductoin is thus accomplished more rapidly by virtue of the large area at grid potential offered by the vanes and the short paths the ions musttake to reach these vanes.

Deionization vanes of this sort may 'be'used in other portions of the tube and are conveniently a'fiixed to the grid cylinder-or .other suitable grid or cathode potential surface such as baffles. For instance, it is often expedient to interpose a number of vanes in the region intermediate the oath ode and the grid. It is common to .employ a lateral baffle member 45 at whose center is a hole; Vanes affixed to this baffle structure may vary in length so that they extend into the region of the hole. Fig. 3 illustrates how this may be done where vanes 46 are mounted on both sides of the bafile plate and extend into the hole. This section also shows annular bracket l3, anode I0 and grid cylinder [9. l

The operation of this thyratron is similar to others well known in the art. Under normal operating conditions, a high positive potential is applied to the anode and the cathode is maintained at ground. The grid potential is'varied; when negative or cathode potentialior possibly slightly'positive), the grid prevents the flow of conduction current within the tube. It is normally apositive potential appearing on the grid which initiates conduction in the tube. Conduction currents in such a gas filled tube take devious paths, e. g., inthis instance from the cathode cylinder 21, around bafile plate 28, through the hole in baflle plate 45, around baille ring 43, through slots [8 in the grid l1 to the anode I 0. The more devious the path, the higher the pulse required to fire the tube, i. e., the greater the control of the grid over tube firing.

Fig. 4 illustrates a tube which is quite similar to the tube of Fig. 1 but which differs in that it may be used more readily at higher voltage levels. Like the tube of Fig. 1 this tube has an anode 10 supported by a flange I l which is sandwiched between annular members l2 and I3. Likewise annular members l2 and I3 are aifixed to tubular insulators l4 and I5 axially located on both sides. of the anode and forming portions of the vacuum envelope. Insulator I5 is essentially the same as I5'in Fig. 1. However, instead of being afllxed to a member corresponding to member 2|, it is afiixed to an annular bracket member 48 which is similar to member 13. Bracket 48 is opposed by annular bracket member 49 similar to member I2. Between the annular brackets is sandwiched radial support member 50 which is similar to support member ll. Radial support member 50 supports tubular auxiliary electrode 5| which extends from the support 50 to an axial level beyond the remote edge of the anode passing between the anode l0 and the grid l1. It is advantageously perforated with elongated slots similar to those in the grid but preferably out of'alignment'with those of the grid so that conduction currents must take a longer, more devious'path to reach the anode and sothat positive ions will have more difficulty bombarding the anode during inverse voltage periods. Dielectric side wall member 54 is aflixed to annular bracket 49 at one edge and to a metal-.- lic terminating member 2| at its other edge. The length and shape of insulation between electrodes may be varied, of course, in order to provide for the particular conditions under which a particular tube is to be used.

The spacing between grid and'anode at high voltages is extremely critical. This spacing must be fixed within a'very narrow range. If itistoo close, field emission can occur. If it is too wide. breakdown will occur according to Paschens Law. As voltage is increased this range grows smaller. Since use of an auxiliary electrode enables wider spacing of adjacent electrodes and/or reduces the potential difference between adjacent electrodes, the problem of field emission ceases to be serious. Likewise, since the path length necessary for breakdown between grid and anode decreases with increased voltage, use of the auxiliary electrodeat an intermediate potential affords shielding of the anode from the grid and actually increases the minimum breakdown spacing between the elements.

To divide the voltage, a resistance divider of high impedance may be located outside of the tube between the anode and cathode with tap connection to theauxiliary electrode, positioned to maintain any desiredpotential. on the auxiliary electrode. Optimum conditions. would obtain where spacings between grid, auxiliary electrode and anodewere equal and the auxiliary electrode was held at a potential midway between that of anode and grid. According to Paschens Law a tube with the auxiliary electrode in nonll. conducting state would withstand about double the voltage obtainable for the same conditions; including the same grid-anode'spacingy in a- -tube' without the auxiliary electrode.

The shielding function of theauxiliary-elem trade is accomplished simply by extending the auxiliary electrode beyond that edge-ofthe anode' cylinder remote from the terminal of the auxiliar-y electrode so that no lines of force extend directly between-grid and'anode. In order tore-- duce electrical stresses between the edge of this element and the grid and in order to better shield the anode the edge of this auxiliaryelectrode 52 is rounded'or curved outward.

Alignment of the-tubular auxiliary electrode-"is relatively simple since the voltage dividing. anode may be first aligned with the anode'and'then fixed in place to the outer vacuum wall in the same manner employed with the anode There? after the grid slotsmay be'aligned with;.:orplaced in opposition to, those in the voltage dividing anode prior to fixing the grid in place: Any number of auxiliary electrodes concentrically arranged may be employed. While many aux: iliary electrodes would produce a more complicat-.- ed assembly problem, it would also affords a means of greatly increasing anode :voltage and. hence the power capacities of the tube. In addi'- tion'to the problem of alignment of perforations, a multi-auxiliary-electrode structure presents a; problem in shielding. Shielding is satisfactory: as long as each auxiliary electrode .shieldsithe surrounding electrodes from the surroundedielec trodes. A voltage dividing electrode may be emeployed with a-planar type: anode, .but' thEiCOmf plication inits positioning andsupport'. would.

probably make such use impractical.

The active grid l'|'- of 'the;Fig. 4 -.tube forms; a segment of the grid cylinder continued bygrid: cylinder i9' which terminatesin springx'fingers."

Spring fingers 22 contact tubular outer;-

22'-. wall termination member 23' whichtis'..sealecl:zto; dielectric wall l4-. Tubulargridrterminallo'; also a continuation of the grid cylinden'issealed to side-wall termination member 2!; at-oneend and to end wall 24 at itsother end. Theactivegrid H has the same outer. diameter as'grid cylinder extension 20' and has 'onetedge'affixed to the wall 2G. Ring "bafile '43. lies iwithinpand is closespaced to the grid slots l8. and may be" afiixed to wall 24'.

The cathode cylinder 21' is supportedsbyrtuebular member 40' joined-to tubular .memberM' by glassring-seal 39'. Tubular member M issealed to grid terminal 2| thus completing the vacuum wall. The internal; assembly; of the cathode is advantageously the samea that of Fig. 1. Atop the cathode ismounted ,baflie plate 28. Between the baffle plate and the grid is -located baffle'plate 45 afiixed to the gridcylinder and having a hole at its center.

The structure of Fig. 4 may also have deionization vanes like those of Fig. 1. Inthecase of both types oftubes, however, other types of deionization vanes may prove'desirable'in many instances. For instance, those shownin 'Fig. 5 provide a tortuous path from any point within the grid ring to the grid slots. When'this type of vane structure is used a ring-type .baflle plate such as 43 or 43 may not-be used. The convolu-- tions. in the vanes 56 and 51, whichdifierin length, minimize the number of ions which .can take a straight path from any point within'the grid ring to. the grid perforation and thence through to the anode during the inverse voltage amnesia;

period. Further'iprotection against :ions lTiS 1rene= dered by thexsmall, individual baffles 58 which" lie ."in front of .the grid slotsxand' each" of which? is afiixed totztheigridadjacenta perforation; Said xbafile' meansseffectively replace the cylin-e clrical baflle 43 of :Fig; .1 .in: adding to .the' grids:

control.

The structure of Figrfiiisexcellent'fonmany' uses but in otherinstances the structure .of Fig: 6

might be preferred; In theFfigafi'construction: vanes 59 of the shape illustrated in Fig; '7 are.

arrangedwithinihe grid-.ring'and aflixed directly-thereto as.in.the:case'of 'the Fig; 5struc-- ture." F'i'g'..8:shows how' the vanes shown in Figs: 6 and 7 mightfit .into;a;gridring"by illustrating; the :activegrid ring-alone showing the slots :for.

receiving the. :vanes... The 'LVSJIES :extend beneath the slots so :that they lie, between: the active grid and the; cathode region; Thus: itis impossiblefor an electronsto come directly "up from the region. between: the:cathode and the :grid. Likewisegitl'is cdifiicult' forrions' not ,extremely closeto the: grid slots to approach theseslotsandpass therethrough; In fact; unless'they are extremely close to the slots, in'orderto. pass'throughithe Bygdoing this' it. is i possible to decrease thedeionization: time: and I. increase the repetition raterof firing the'tube; Becausethey tend to partially-block conduction paths, the deionization-tvaneshave some of .the characteristics and actdtoisome 'extentlike baffies'in thatthey increase the amount of grid control. Thus when deionizationvanes are used other baffling may be largely omitted lest the grids have too much control so that .too. muchyoltagemust be applied to 1- trigger .the tube.

By the'zsame token my invention introduces a novel means of bafiling in"thyratrons. My. in-. vention provides individual baffling for each perforationpin the grid or attleast presentsithe same amount and kindof bafiling foreach perforation- That is to samyunlike the priorart .bafiles which. covered a.- whole active: grid area; mybafiles cover only the minimum. area necessary for. control, 1. e., .the'perforationsiand adjacent regions. Thusconduction streams through different perforations do not have to travel different distances between cathode and anode around a, single baffie covering all perforations. The path length between cathode and anode through any perforation is essentially the same. My invention achieves this end by the use of baiiling means over orin front of each perforation inthe active grid which extends the same distance beyond each perforation in the region where conduction currents pass; several means. In the Fig; 1 type tube a' concentric tubular bafil'e as shown maybe. used; Where "the more complicated deionization vanes are used,;,however,' it'is necessary to mount in,-- dividual baflles. adjacent each perforation.as-:in

The fact that these- I. achieve' this .end. by-

the Fig construction oruse a portion of the deionization vane to the same" end as in Fig. 6.

Thus it is possible thatdeionization vanes may serve as bailles just as baiiiesalways serve as,

deionization means. In this connection it will be noted that my bafile means are particularly valuable in reducing bombardment of the anode by positive ions during inverse voltage periods.

Many of the features of my invention are equally applicable to planar anode thyratrons as they are to my novel cylindrical geometry. To be more specific the cathode structure; the deionization vanes and the bafile means may all be employed in planar as well as cylindrical geometry thyratrons. Fig. 9 illustrates how mynovel cathode may be 5 used in such a tube and in addition illustrates an adaptation of my novel bafiling means. planar thyratron of Fig. 9 is advantageously operated with the grid grounded. This thyratron employs baffles 6i and 62 having portions eXtend-- ing perpendicular to the plane of the grid and portions affixed thereto extending-'parallelto the grid and overlying the perforation. These members are made to overlap one another so that con- .duct'ion currents will have to take a' devious path 1 in' order to reach the anode. The close proximity of'vane 62 to the grid slot reduces the ions which pass through the grid slot and bombard the anode during the inverse voltage period. However, as

f i'llustrated a large pulse would be required to tri er the tube. Omission of either bafile 6| or 62fwould reduce the amount oftrigger required. As mentioned, this tubecontains the same genferal type of tubular'cathode as the Fig. 1 structur with a cathode cylinder 21" 'topped'by baffle plate 28". However, the tubeenvelop'in this instance is uniquein that it is also the-grid cylinder l9" which ma'y-extendthe full lengthof the tube. The cathode is afiixed to this cylinder by means of tubular sleeves 40" and l l" sealed to ring seal 39". Thus cleanup o'f the'gas maybe avoided by positioning insulator 39" close to grid I9 The rest ofthe structure differs from the cylindrical variation. The anode 64 is planar and has an axial rod support conductor 65afiixed to to it. Insulator 66 between anode lead 65'and tubular member 61; which is sealed'to theend of grid cylinder IB forms the end-wall vacuum lclosurej" "The active grid in this instance is a planar member 68 which has perforations 159-- which are baffled as aforementioned by vanes BI and 62. The active grid is sealed in place to the gridfcylinder at a'spacing which-does not exceed the minimum -value' for-breakdown between grid and anode underthe particular-conditions .ex- *istent in that tube. anode is close spaced from shieldin member which is terminated in a tubular flange 10a.- which The inactive 1 side ofthe fits around tubular glass flange 66a which-,in

-turn, extends from insulator end-closure. 66.

,In essence this tube operates essentially as the tubes shown in Figs. land 4. It'issubject: to many of the disadvantages encountered in, planar 1 tubes above enumerated, such as difficultieswith .anode dissipation,proble ms of grid buckling,.1etc.'

However, with such a low inductance grid lead,

it is advantageous to ground the-gridand fire the tube bya-negative trigger onthecathode, Such operation eliminates the high voltage grid spike due to the conductive coupling between grid and anode'during the initiation .of the dischargewith trigger circuit. In addition, less bafiling between anode and cathode may normally beused because iotthe low impedance between grid and the nega- "tive return lead of the plate power supply. This amounts to improved efliciency and low anode dissipation. l

I claim;

1. An electron tube comprising a vacuum envelope filled with low pressure gas and having thereinan anode, an emitting cathode, a grid wall between the anode and the cathode which has perforations therein opposing the anode and the edges of which terminate at portions of the vacuum envelope, bafile means so positioned be- 'tween cathode and grid and close to the grid perforations that the path lengths between cathode and anode through each grid perforation are substantially equal, metallic deio-nization vanes affixed to portions of the grid, and auxiliary electrodes between the grid and the anode having perforations therethrough.

'2. An electron tube comprising a vacuum envelope filled with low pressure gas and having therein a cylindrical anode, an emitting cathode, a cylindrical grid wall between the anode and the cathode which has perforations therein opposing the anode and the edges of which terminate at-portions of the vacuum envelope, baflle means so'positioned between cathode and grid and close to the grid perforations that th path lengths between cathode and anode through each grid perforation are substantially equal, metallic deionization vanes affixed to portions of the grid and cathode, and cylindrical auxiliary electrodes between the grid and the anode having perforations therethrough.

3. A coaxial tube structure comprising a vacuum envelope filled with low pressure gas and having therein a cylindrical anode, an integral cathode assembly consisting of a tubular cathode to which emitter is applied and a high inductance filamentary heater lying coaxially within the tubular cathode, a cylindrical grid wall between the anode and the cathode which has perforations therein opposing the anode and the edges of which terminate at portions of the vacuum envelope, baffle means so positioned between cathode and grid and close to the grid perforations that the path lengths between cathode and anode through each grid perforation are substantially equal, metallic deionization vanes afiixed to portionsof the grid and cathode and extending into the space between the grid and cathode, and cylindrical auxiliary electrodes between the grid and the anode shielding said anode from the grid and having perforations therethlrough in .the region of the grid perforations.

4. An electron tube comprising a vacuum envelope filled with low pressure gas and-having therein a cylindrical anode, an emitting cathode,

its accompanying problem of feedbackinto the and a grid cylinder lying between cathode and anode which has perforations. therein opposing .the anode and both ends of which terminate-at the vacuum envelope. I

j '5. An electron tube comprisinga vacuum en-. velope filled with low pressure gas-and having therein a cylindrical anode, an emitting cathode,

and a grid cylinder lying between the cathode andtheanode which has perforations therein opposing the anode, said grid cylinder being .anixed at one end to the vacuum wall and making sliding contact with vacuum wall at the opposite end.

16. An electron tube comprising a vacuum envelope filled with low pressure gas and having therein a cylindrical anode supported by the envelope side walls, an-emitting cathode; anda .grid cylinder lying between the cathode and the anode which-has i perforations therein opposing theanode, said cylinder being aflixed at .oneend to the vacuum wall and making Sliding-contact with vacuum wall at the opposite end;

l 7. An electron tube comprising a vacuum envelope filled with low pressure gas and havin :therein a cylindrical anode supported by a highly :conductive annular member penetrating the envelope side walls, an emitting cathode, and a grid cylinder lying between the cathode and the --anode which has perforations therein opposing the anode, said cylinder being affixed at one end to the vacuum wall and making sliding contact -with the vacuum wall at the opposite end.

8.- An electron tube comprising a vacuum -en'velope filled with low pressure gas and having therein a cylindrical anode supported by the envelope side walls, an emitting cathode, anda grid cylinder lying.' between the cathode and theanode which has perforations therein oppos- -ing the anode, said cylinder being affixed at one end to the vacuum wall and making sliding contact'with the"vacu'um wallat the opposite end, the sidewalls of saidva'cuum'envelope consisting of--tubular'-insulators, said insulatorshaving a regions grid cylinder between cathode and-anode which cylinder has a low heat flow impedance portion "at one end, perforations through an adjacent portion of the cylinder opposing the active anode and resilient contact means at the other end of the' cylinder, the side walls of said vacuum en- 'velope consisting of tubular insulators, said "insulators having a spacing to the grid cylinder 'approximatelythe same as the gridanode spacing and tubular metallic members seale'd to said -="insulators at both ends of the tube, one of said members being in turn sealed to the low heat flow impedance portion of the grid cylinder and the other member furnishing a contact surface: io'r the resilient contact means at the other end of 'the grid cylinder. v v 10. An, electron tube comprising a cylindrical anode supported by a highly conductive annular member penetrating the vacuum envelope side walls, an emitting cathode, a grid cylindrbetween cathode and anode which cylinder has a low heat flow impedance portion at one end, perforations through an adjacent portion of the -cylinder opposing the active anode and ISSil-r ient contact means at the other end of the cylinder, a vacuum envelope enclosing said elements filled with low pressure gas and consisting of side walls. composed of tubular insulators, said insulators having a spacing to the grid cylinder-approximately the same as the gridanode spacing, tubular metallic members sealed to said insulators at both ends of the tube, one of the said members being in turn sealed to the low heat flow impedance portion of the grid cylinder and the other member furnishing a contact surregion of the grid and the end of the cylinder sealed to the envelope side walls, and closure -means including the cathode assembly sealed to the opposite end of the envelope side walls.

1 l.-.An electron tube comprising a .vacuum ring being close'spaced at all points to a-metallic envelope filled with'low pressure gas and having therein van anode-a grid cylinder having 'a perforated region opposing the anode, and an integral cathode assembly consisting of a tubular cathode to which emitter is applied, sealing means between the cathode and a grid-potential tubular member including a dielectric ring, said dielectric ringi being close spaced at all pointsto metallic members, sealing means including a dielectric ring closing the end of the cathode cylindenand heater means within said cathode.

12. An electron tube comprising a vacuum envelope filled with low pressure gas and, having therein an anode, agrid cylinder having a perforated region opposing the anode, and an integral cathode assembly consisting of a tubular cathode to which emitter is applied, sealing means between the cathode anda grid potential tubular member including a dielectric ring, said dielectric ring being close spaced at all points 'to a metallic member, sealing means including a dielectric ring closing the end of the cathode cylinder, and heater means within said. cathode consisting of a high inductance filament axially cylinder and at the other end to a lead coaxial disposed and connected at one end to the cathode with the cathode cylinder which leadpenetrates the sealing means closing the end of-the cathode cylinder. v

13. An electron. tube comprising a vacuum envelope filled with low pressure gas and having therein an anode, a grid cylinder having a perforated active grid opposing the anode, and an integral cathode assembly consisting of a tubular cathode to which emitter is applied, an axially disposed bafiie located at and serving to partially close the end of the cathode cylinderinternal-of the tube -to which end said 'bafile-ds connected,

sealingmeans between the-cathode and the grid cylinder including a dielectric ring, said dielectric tube member, sealingmeans including azdielectric ring closing the end of the cathode cylinder and heater means'within said cathode consisting of a helically wound filament-coaxially disposed within the cathode and connectedat one end the cathode cylinder.

'to the cathode bafileand atthe otherend toga lead coaxial with the cathode cylinder which lead penetrates the sealing means closing the end of 14. An electron tube comprising a vacuum envelope filled with low pressure gas and having therein an anode, agrid cylinder having a perforated active gridtopposing the anode, and

an integral cathode assembly consisting of a tubular cathode to which emitter is applied, sealelectric ring closing the end of the cathode cylinder, and heater means within said cathode.

15. An electron tube comprising a vacuum envelope filled with low pressure gas andhaving therein an anode, a grid cylinder having a perforat'ed active grid opposing theanode, and an "integral cathode assembly consisting of a tubular cathode to which emitter is applied, sealing means between the cathode and the grid cylinder including a dielectric ring, said dielectric 'rin'g being close spaced at all points to a grid potential cylindensealing means including a dielectric ring closing the end of the cathode cylinder, and heater means within said cathode consisting. of

a high inductance filament axially disposedand connected at one end to the cathodecylinder and at the other end to a lead, coaxial with the cathode cylinder which lead penetrates the sealing means closing the endof the cathode cylinder.

16. An electron tube comprising a vacuum envelope filled with low pressure gas and having therein an anode, a grid cylinder having a perforated active grid opposing the anode, and an integral cathode assembly consisting of a tubular cathode to which emitter is applied, sealing means between the cathode and the grid cylinder including a dielectric ring sealed at both edges to metallic sleeves, said dielectric ring being close spaced at all points toa grid potentialcylinder, sealing means including a dielectric ring closing the end of the cathode cylinder, and heater-means within said cathode.

17. An electron tube comprising a vacuum'envelope filled with low pressure gas and having therein an anode, a grid cylinder having a perfora-ted active grid opposing the anode-and an integral cathode assembly consistingof atubular cathode to which emitter is applied, an axially disposed bafile located at and serving to partially close that end of the cathode cylinder internal of the tube, sealing means between the cathode and the grid cylinder including a dielectric ring sealed at both edges to metallic sleeves saiddielectric ring being close spaced at all points to a grid potential cylinder, sealing means including a dielectric ring closing the end of the cathode cylinder, heater means within said cathode consisting of a helically wound filament axially disposed and connected at one end .to the axially disposed baffle and at the other end to a lead coaxial with the cathode cylinder which lead penetrates the sealing means closing-the end of the cathode cylinder.

18. An electron tube comprising a vacuum envelope filled with low pressure gas and having therein an anode, an emitting cathode, a grid wall between the anode and the cathode which has perforations therein opposing the active anode and baflle means so positioned between cathode and grid, close to the grid, that it permits equal path lengths between cathode and anode through each grid perforation.

19. An electron tube comprising a vacuum envelope filled with low pressure gas and having therein an anode, an emitting cathode, a grid wall between the anode and the cathode which has perforations therein opposing the active anode and baffle means between cathode and grid, close to the grid, said baiiie means terminating at equal distances from their respective perforations.

20. An electron tube comprising a vacuum envelope filled with low pressure gas and having therein an anode, an emitting cathode, a grid wall between the anode and the cathode which has perforations therein opposing the active anode and baiile means between cathode and grid in front of and close to the grid perforations, said means terminating at equal distances from their respective perforations, so that the current paths etween cathode and anode through all of the perforations are essentially the same length.

21. An electron tube comprising a vacuum envelope filled with low pressure gas and having therein an anode, an emitting cathode, a grid wall between the anode and the cathode which has perforations therein opposing the active anode, and battle means between cathode and grid in front of each perforation, said means being supported by the grid adjacent each perforation.

22. An electron tube comprising a vacuum en-. velope filled with-low pressure gas and'having therein a cylindrical anode, an emitting cathode, acylindrical grid wall between anode andcathode which has perforationstherein opposing the active anode, and baffle means between, cathode and grid in front of .each perforation, said means being supportedadjacenteach perforation.

23. An electron tubecomprising a vacuum envelope filled with lowpressure gas and having therein a cylindrical anode, an emitting cathode, a cylindrical grid wall between anode and cathode which has perforations therein opposing theactive anode, and a cylindrical baffle coaxially located within the grid in front of the perforations. H

24. An electron tube comprising a vacuum envelope filled with low pressure gas and having therein a cylindrical anode, an emitting cathode, a cylindrical grid wall between anode and cathode which has perforationstherein opposing the active anode, and individual bafile means in front of each perforation supported-by the grid adjacent each perforation." 7

i 25. An electron tube comprising a vacuum envelope filled with low pressure gas and having therein an anode, an emitting cathode, a grid wall between the anode and the cathode which has perforations therein opposing the active anode, and metallic deionization vanesafiixed to portions of the grid and cathode-extending into the region between the cathode and the grid.

' '26. An electron tube comprising a vacuum envelope filled with low pressure gas and having therein a cylindrical anode, an emitting cathode, a cylindrical grid wall between the anode and the cathode which has perforations therein opposing the active anode, and metallic deionization vanes afiixed to a grid potentialsurface" and extending into the grid-cathode region.

27. An electron tube comprising a vacuum envelope filled with low pressure gas and having therein a cylindrical anode, an emitting cathode, a cylindrical grid wall between the anode and the cathode which has perforations therein opposing the actlve anode, and metallic deionization vanes affixed to the grid in the region of perforation and extending tortuously toward the tube axis.

28. An electron tube comprising a vacuum envelope filled with low pressure gas and having therein a cylindrical anode, an emitting cathode, a cylindrical grid wall between the anode and the cathode which has perforations therein opposing the active anode, and deionization vanes which also serve as baflie means consisting of metallic members affixed to the grid in the region of perforation so that they partially block the perforations and extend tortuously toward the tube axis.

29. An electron tube comprising a vacuum envelope filled with low pressure gas and having therein a cylindrical anode, an emitting cathode, a grid cylinder lying between cathode and anode which has perforations therein opposing the active anode and both ends of which terminate at the vacuum envelope, and a tubular coaxial auxiliary electrode between grid and anode having perforations therethrough.

30. An electron tube comprising a vacuum envelope filled with low pressure gas and having therein a cylindrical anode supported by the envelope side walls, an emitting cathode, a grid cylinder lying between the cathode and anode which has perforations therein opposing the ac- 19 tive anode; said cylinder being aflixed at one end to; the vacuum wall and making sliding contact with the vacuum wall at the opposite end, and a tubular'coaxial electrode between grid and anode having perforations therethrough, said electrode being supported by the envelope side walls.

31. An electron tube comprising a vacuum envelope filled with low pressure gas and having therein a cylindrical anode supported bythe envelope side walls, an emitting cathode, a grid cylinder lying'between the cathode and anode which has perforations therein opposing the active anode, said cylinder'being afiixed at one end to the vacuum wall and making sliding contact with the vacuum wall at the opposite end, and a tubular coaxial electrode between grid and anode having perforations therethrough, said electrode being supported'by the envelope side walls by means affixed near one end thereof; the other end of the electrode extending below the adjacent surrounding electrode thereby shielding said surrounding electrode from the adjacent surrounded electrode and from all elements which said surrounding electrode surrounds.

32. An electron tube comprising a vacuum envelope filled with low pressure gas, the envelope side walls being a metallic grid cylinder, an anode supported by one end wall; an emitting cathode supported by the other end wall, and a perforated grid-pbtential member lying between said anode and said cathode.

33. An electron tube comprising a vacuum envelope filled with low pressure gas, the envelope side walls being a metallic grid cylinder, a planar anode supported by one end wall, an emitting cathode supported by the other end wall, and grid potential members surrounding said anode, that portion of said members between the cathode and grid having perforation therethrough.

the anode, that member-between cathode and anode being perforated and that on the other side being annular and having an inner edge which terminates on an extension of the dielectrio portion of the end well. i

'35. An electron tube comprising a vacuum envelope filled with low pressure gas, the envelope side walls being a metallic grid cylinder, a planar anodeextending radially from an axial support which is sealed through one end Wall, a tubular emitting, cathode assembly forming the closure at the other end of the tube sealed to the grid cylinder by means including a dielectric ring which is close spaced to the grid cylinder and including a high impedance heater filament disposed coaxially within the cathode, planar grid potential members on both'sides of the anode, that member between cathode and anode being perforated and that on the other side being annular, its inner edge terminated on an, extension of the dielectric portion of the end wall and bafile means disposed in front of each of the grid perforations, and supported by means adjacent each Perforation.

HOWARD D. DOOLI'ITLE No references cited. 

